I was asked a question the other day that applied when I was apprenticing but I havn't seen it lately.

There was a time (maybe still is) when it was reqired to have the bathroom exhaust fan on the three way switch. One switch outside and the other inside the washroom.

I do very little residential and am unsure as to weather this rule still applies. If it does, can someone tell me where this rule came from and what its intent was. I remember asking one of my teachers who just danced around the question. I concluded at the time that he didn't actully know.

Never heard of that before. The only reason you would use a three way switch for an exhaust fan for a bathroom is if you had two bathrooms and they are exhausted by the same fan. Regular bathroom fan you only need one switch. Outside or inside it doesn't matter. I perfer inside.

This is still common practice. A better method that we use is two single pole switches wired in such a way that if either of the two switches is turned on, the fan would run.

The one switch would be located obviously in the bathroom, the second switch would need to be located at or near the wall thermostat.

This is a building code requirement, not a ESA or code book requirement.

The reason : Today's new homes are built more air tight then ever before. Because of this, building code requires some sort of "air exchanger" in each premises. More often than not, the bath fan controlled by these switches will be larger (90 or more cfm) compared to the other bath fans on the premises which are usually 50-60cfm. The large fan will most likely be located in the central or biggest bathroom of the residence.

If the home owner decides to get a proper Air Exchange unit (HRV), then the double switch requirement is exempt in the Ontario Building Code.

My 2 cents, I think this is just a band-aid solution to having a proper air exchanger in a house. I haven't met a single homeowner who regularly uses this method. If anything, I get numerous calls from homeowners asking me what this switch is by their thermostat and what it controls.

In Alberta, the Alberta Building code section 9.32.3.4 requires that the principle exhaust fan, be it the bathroom fan or say a hallway exhaust fan,which ever basically is the largest CFM unit is to be interconnected in a way that the activation of this fan automatically activates a supply fan or furnace fan on hot air heating systems,the supply fan must introduce air in quantitys equal to the air exhausted.

(2) Except as permitted in Sentence (3), the principal exhaust fan shall be controlled by a manual switch.

(3) A principal exhaust fan required under this Articlem may be controlled by a dehumidistat or other automatic controldevice where the manual switch required in Sentence (2) is capable of activating the fan regardless of the setting of theautomatic control.

(4) The switches required in Sentences (2) and (3) shall be centrally located in the dwelling unit and shall be identifiedwith the words VENTILATION FAN.

(5) The principal exhaust required in this Article may be provided by means of a heat recovery ventilator installed in accordance with Article 9.32.3.11.